This invention relates to the measurement of the mechanical properties of highly flexible or limp sheet material, for example paper, textile material, plastics and composite materials. In particular, the invention relates to the measurement of the tensile, shear, buckling, and compression strengths, sheet thickness, bending stiffness and surface qualities such as friction and roughness. The purpose of such testing, under normal loading without destruction of the sample of the material under test, is to determine the performance of the material in use, e.g. clothing fabrics during normal wear.
To date, such measurements have generally been made independently on different samples of the material to be tested. For example, there is the widely accepted Kawabata Evaluation System for Fabric (KESF) for textile fabrics. With this system, different samples of the fabric to be tested are required to be placed in several different devices in order to make the measurements of the various properties listed above. One sample of the fabric to be tested is placed in a device which measures tensile and shear properties by clamping the sample at two spaced locations and moving the clamps apart and laterally relative to each other. This device has to be calibrated for each measurement on a sample. Bending strength, but not buckling, is measured by placing a different sample of the fabric in a second device. In this device the sample is mounted vertically and the device is very difficult to set up in trying to achieve an even tension in the fabric. One clamp makes a circumferential movement in order to measure the bending strength. Thickness measurement requires another measuring device. In this case a head moves vertically relative to the fabric in order to measure the thickness of the material and then its compressibility. For surface properties, a further sample of the material is clamped under load in a further device in which a head lowers and the material is then moved laterally relative to the head. Different probes on the head measure surface roughness and friction. It is very expensive to have all of these devices and very time consuming to place the different samples in the different devices in order to make all of the measurements. Another system is the Fabric Assurance by Simple Testing (FAST) system.
This is a simplified version of the KESF system, but at least two different samples are needed.
Thickness and compression are measured in one device at two positions of a movable head.
Bending is measured in another device in which the fabric is laid on a bed and is traversed by a moving plate on top of the fabric until the fabric extends over the edge of the bed and cuts a light beam. For tensile strength, the fabric is placed between two clamps in a further device, the lower one of the clamps being on an arm which is pivoted and has a weight on the other end. When the arm is released, the device registers the load in the fabric. The results from these tests are limited to the measured loads only and cannot provide full stress/strain profiles of the test samples. In addition the results from the two test systems are not very reproducible, due to the need for different sample sizes and the manual handling for each test. In the cosmetics and medical fields it is desirable to determine the effect cosmetic or medical creams and the like have on the human skin. To this end a fabric which has similar characteristics to human or animal skin is treated with the cream and the mechanical properties of fabric are then measured. For such an application the KESF and FAST systems are considered too expensive and too complicated.
It is an object of the present invention to provide a single apparatus for the measurement of the mechanical properties of a single sample of a limp sheet material in order to reduce the equipment costs compared with that of the number of existing devices required. It is also an object of the present invention to reduce the time and complexity of making such measurements and to increase the accuracy and reproducibility of such measurements compared with the existing methods.
The invention provides a device for the measurement of the mechanical properties of a limp sheet material, comprising a base, a pair of clamping members operable to clamp the sheet material to the base at spaced locations, load sensing means on at least one clamping member, at least one of the clamping members being movable away from and towards the other in the plane of the sheet material and laterally of the other in said plane, and a head assembly having a sensing device spaced from the base and movable theretowards and laterally of the plane of the sheet material.
One clamping member may be the at least one movable clamping member and the load sensing means may be mounted on the other clamping member. Two load sensing means having differing ranges of measurement may be mounted on the one clamping member, the first load sensing means being adapted to measure tensile load and the second load sensing means being adapted to measure buckling load. The measurement device may comprise a third load sensing means adapted to measure shear loads. The sensing device may comprise a further load sensing means and a surface characteristics sensing means.
Preferably the base is a plate which is disposed substantially horizontally, in which case the clamping members may be disposed above the base plate and positionally adjustable to clamp the sheet material. The measuring device may comprise position indicating means adapted to indicate the position of the at least one movable clamping member relative to a datum position. The at least one movable clamping member may be mounted on low friction slideways, and the slideways may be disposed remote from the axes of movement of the at least one movable clamping member. The head assembly may be disposed between the clamping members, and may be mounted on the base plate. The head assembly may comprise a slide part on which the sensing device is mounted for movement towards the base plate and, together with the slide part, laterally of the sheet material.
The base plate may have an edge to a side of the at least one movable clamping member remote from the other clamping member, over which edge the sheet material may be moved to cantilever thereover. The measurement device may comprise a beam transmitting device and a beam sensing device operable to receive the transmitted beam and detect when the sheet material interrupts the beam. The beam may be directed from beneath and spaced from the edge of the base plate at an angle of between 30xc2x0 and 60xc2x0 to the horizontal.
Preferably the beam is directed at an angle of 41.5xc2x0 to the horizontal. The base plate may be formed to have a shallow recess between the spaced locations to reduce the frictional contact between the sheet material and the base plate.
The measurement device may comprise control means operable to control the sequence of movement of the at least one movable clamping member and the sensing device. The control means may also be operable to render operable the first or second load sensing means for measuring tensile load or buckling load respectively dependent on the direction of movement from the datum position of the at least one movable clamping member. The control means may be operable to vary the length of time between successive movements of the at least one movable clamping member and the sensing device. The control means may also be operable to adjust the speed of movement of the at least one movable clamping member and the sensing device. The control means may comprise programmable means for the selection of the measurements to be made, the speed of movement of the at least one movable clamping member and the sensing device, and the timing of the movements.
The movement of the at least one movable clamping member and the sensing device may be effected by respective stepper motors. The clamping members may also be moved between respective sample material release positions and their clamping positions by respective stepper motors.
In another aspect, the invention relates to methods and apparatus for the assessment of seam pucker and other surface irregularities.
Assessment of surface irregularities, particularly seam pucker, is at present largely a subjective matter. Attempts to introduce objectivity into the assessment have, to date, not been so successful as the result is non-standard. The same is true for measurements, generally, of surface irregularities of which seam pucker is typicalxe2x80x94with the exception, possibly, of microscopic surface roughness measurements, necessarily automated and standardized because of inaccessibility to the naked eyexe2x80x94surface irregularity is xe2x80x9cjudgedxe2x80x9d rather than objectively measured.
The invention provides an objective assessment for seam pucker and other, comparable surface irregularities.
The invention comprises a method for the assessment of seam pucker and other surface irregularities comprising directing at the surface a line beam from an illuminator, imaging the line on the surface formed by the line beam and analysing data of the image to produce an objective indication of the degree of irregularity of the surface.
Parallel line beams may be directed at the surface. For the assessment of seam pucker, the parallel line beams may be directed to form lines on the surface parallel to and either side of the seam, and at an angle from the plane perpendicular to the surface.
The illuminator may comprise a line beam laser.
The line on the surface may be imaged by a pixel image such as a CCD array camera.
The image may be analysed in a computer programmed with image analysis software. The result of analysing the image may be a display of a distribution of severity of deviation of the surface from flat.
The surface may be that of a limp material, such as a textile fabric, mounted on a flat support base. The base may, for the assessment, be inclined steeply with the material clamped uppermost and resting against the base below the clamping location.
For consistency of measurement the material is preferably the same size as the bed, so no additional irregularity is occasioned by edge effects. A sample for assessment may be cut to size using the bed as a template.
The invention also comprises surface irregularity assessment apparatus comprising
a line beam illuminator;
a support arrangement for the surface under assessment such that the line beam illuminator is directed at the surface to illuminate a line thereon;
an imaging arrangement adapted to image the line illuminated on the surface, by the line beam illuminator; and
analysis means adapted to receive image data to produce an objective indication of the degree of irregularity of the surface.
There may be one, two or more line beam illuminators casting parallel beams. Beams may be cast in different arrangements to provide further information.
The imaging arrangement may comprise a pixel imaging arrangement, and may comprise a CCD array.
The line illuminator may be a laser.
The analysis means may comprise a computer programmed with image analysis software.